Illegal Immigration and Fence Posts
The current liberal take on immigration is quite simple: We must keep it illegal but cannot enforce the law. This has the long-term effect of producing a large resident population who are dependent on the good will of liberals. More generally, unenforced laws that aren't repealed have a similar effect. According to a comment at Samizdata:
The problem is, they will outlaw almost everything while enforcing very little. Imprisonment by stealth. People will not know they are encircled until it is too late - like putting in all these very deep, robust fence-posts with no fence panels. All seems open. One day you will wake up and the panels are in, you are trapped and they can decide what law they wish to impose to nail whomsoever they desire.They couldn't do that if the law were either repealed or enforced. If it were enforced we would have fewer illegal residents and those we did have would be far more cautious.
In particular, if an ethnic group with a lots of illegals tries leaving the “plantation,” the people on the next Journolist will coordinate reasons to start cracking down on them (e.g., they're homophobic, they're overpopulating the U.S., they're busting unions, etc.) It won't be any more difficult than the leftist about face on Israel over the past generation or two. It you want a specific example, consider the case of Elian Gonzalez. It was the left who called for his deportation.
By the way, the goal of having blackmailable residents will be helped by abandoning birthright citizenship.